It’s good to have all Sitecore environment well maitained and cleaned.

On one of the solutions (see picture above), I found that the log file is splitted by size. It caused that extension is not txt but a number.
Generally, it’s not an issue, but if you look on default Sitecore Cleanup Agent configuration, by default, only *.txt files are removed not *.txt.[NUMBER].

But you can quickly patch Cleanup Agent settings and configure your cleaning task as you need. Below you can find an example:
<?xml version="1.0" encoding="utf-8" ?>
<!--
Purpose: This is an example how to modify CleanupAgent base on environment rule.
-->
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/" xmlns:role="http://www.sitecore.net/xmlconfig/role/"
xmlns:env="http://www.sitecore.net/xmlconfig/env/" xmlns:set="http://www.sitecore.net/xmlconfig/set/" >
<sitecore>
<scheduling>
<agent type="Sitecore.Tasks.CleanupAgent" method="Run" interval="06:00:00" patch:instead="*[@type='Sitecore.Tasks.CleanupAgent']" env:require="!PROD">
<!-- Specifies files to be cleaned up.
If rolling="true", [minCount] and [maxCount] will be ignored.
[minAge] and [maxAge] must be specified as [days.]hh:mm:ss. The default value
of [minAge] is 30 minutes.
[strategy]: number of files within hour, day, week, month, year
[recursive=true|false]: descend folders?
-->
<files hint="raw:AddCommand">
<remove folder="$(dataFolder)/logs" pattern="*log.*.txt*" maxAge="10.00:00:00" recursive="true" />
<remove folder="$(dataFolder)/diagnostics" pattern="*.*" maxAge="10.00:00:00" recursive="true" />
<remove folder="$(dataFolder)/viewstate" pattern="*.txt" maxAge="2.00:00:00" recursive="true" />
<remove folder="$(tempFolder)/diagnostics" pattern="*.*" maxAge="00:10:00" recursive="true" />
<remove folder="/App_Data/MediaCache" pattern="*.*" maxAge="90.00:00:00" recursive="true" />
</files>
</agent>
</scheduling>
</sitecore>
</configuration>
This and more patch examples you can find in repository: